NMR and EPR Spectroscopic Identification of Intermediates Formed upon Activation of 8-Mesitylimino-5,6,7-trihydroquinolylnickel Dichloride with AlR2Cl (R = Me, Et)

The intermediates formed upon activation of 8-mesitylimino-5,6,7-trihydroquinolylnickel dichloride [LNiCl 2 ] with AlR 2 Cl (R = Me, Et) have been studied by 1 H NMR and EPR spectroscopy. Activation of LNiCl 2 with AlEt 2 Cl has been shown to afford diamagnetic ion pair [LNi II Et] + [AlEt 3 Cl] −, whereas the use of AlMe 2 Cl as activator yields the paramagnetic ion pair with proposed structure [LNi II (μ-R) 2 AlMeCl] + [AlMe 3 Cl] − (R = Cl or Me). With time, both ion pairs convert to bis-ligated Ni(I) complexes with proposed structures [L 2 Ni I ] + [A] −, where [A] − = AlEt 3 Cl – or AlMe 3 Cl –, respectively. Ethylene reactivity examination reveals that ion pairs [LNi II Et] + [AlEt 3 Cl] − and [LNi II (μ-R) 2 AlMeCl] + [AlMe 3 Cl] − are the closest precursors of the active species of polymerization.